Computing devices often send data to and receive data from other computing devices via a network. This is commonly accomplished, in part, by creating a layer 3 (L3) internet protocol (IP) packet that includes, at least, the data to be communicated and a source and destination IP address. The packet is then encapsulated in a layer 2 (L2) media access control (MAC) frame that includes, at least, the packet and a source and destination MAC address. Information included in the MAC frame (e.g., source IP address, destination IP address, source MAC address, destination MAC address) allows network devices that exist between the sending and receiving computing devices to determine the intended destination of the MAC frame in order to transmit the MAC frame to the appropriate next-hop on the path to the destination computing device of the MAC frame.
In a virtual extensible local area network (VXLAN) environment, MAC frames are sent from and received by computing devices, in part, via VXLAN tunnel end points (VTEPs) to which a computing device is operatively connected. To send a MAC frame on behalf of a sending computing device, a sending VTEP must know the IP address of a receiving VTEP that is operatively connected to the computing device identified as the destination of the MAC frame via a destination MAC address (i.e., a MAC-to-VTEP mapping). In order to transmit a MAC frame to the receiving VTEP (which will, in turn, transmit the MAC frame to the appropriate destination computing device), a sending VTEP encapsulates the MAC frame in a VXLAN frame in which the IP address of the remote VTEP becomes the destination IP address of the VXLAN frame. This VTEP IP address is used (along with other information in the VXLAN frame) to transport the VXLAN frame through a network until the VXLAN frame reaches the receiving VTEP, which extracts the original MAC frame from the VXLAN frame and transmits the MAC frame to the computing device identified by the destination MAC address of the original MAC frame.
According to the VXLAN Draft Specification, when the MAC-to-VTEP mapping is not known by a VTEP for a destination computing device, the MAC frame is encapsulated in IP multicast and flooded throughout the VXLAN domain, improving the likelihood that a frame arrives at the VTEP that is operatively connected to the destination computing device, while incurring the cost of delivery to potentially many other VTEPs